Low-floor electric vehicle

ABSTRACT

The invention provides for a high occupancy or heavy-duty vehicle with a battery propulsion power source, which may include lithium titanate batteries. The vehicle may be all-battery or may be a hybrid, and may have a composite body. The vehicle battery system may be housed within the floor of the vehicle and may have different groupings and arrangements.

CROSS-REFERENCE

This application is a continuation application of U.S. patentapplication Ser. No. 14/992,900, filed Jan. 11, 2016, which is acontinuation application of U.S. patent application Ser. No. 13/887,135,filed May 3, 2013 (now U.S. Pat. No. 9,252,417), which is a continuationapplication of U.S. patent application Ser. No. 12/459,074, filed Jun.26, 2009 (now U.S. Pat. No. 8,453,773), which claims the benefit of U.S.Provisional Application No. 61/076,480, filed Jun. 27, 2008, whichapplications are entirely incorporated herein by reference.

STATEMENT AS TO FEDERALLY SPONSORED RESEARCH

This invention was made with the support of the United States governmentunder the National Fuel Cell Bus program, Project ID numbers GA-04-7001,GA-04-7002 by the Federal Transit Administration (FTA).

BACKGROUND

In recent years, hybrid and electric vehicles, which are provided with abattery, have been proposed, and some of them have been put intopractice, to effectively use energy, in particular, regenerative energyas environmental measures. Typically, secondary batteries, which havebeen put to into practice and installed in vehicles so far, include, forexample, lead storage batteries, nickel metal hydride batteries, or highpowered lithium ion batteries.

The use of such batteries provide many challenges such as thermaldegradation, or the requirement of significant volumes or space due tolow capacity. Such batteries may be heavy, which can lead to decreasedperformance of vehicles. Furthermore, the active materials of theelectrodes are low in the rate of occluding and discharging ions, andhence efficient charging cannot be achieved during fast charging, eitherform a stationary charger of regenerative charging. The speed ofregenerative charging can be very pertinent for a heavy-duty vehicle,such as a bus, that may be regularly recharged within small time frames.

Thus, a need exists for a heavy-duty vehicle with a battery systemcapable of rapid charging. A further need exists for a heavy-dutyvehicle that can efficiently utilize its battery system.

SUMMARY OF THE INVENTION

The invention is directed to a heavy-duty vehicle, such as a bus, with apower source capable of being fast-charged. In one aspect of theinvention, the power source may include a lithium titanate batterysource. In some instances, an additional power source may be provided. Apower source may comprise one or more battery packs. The power sourcemay be housed in the floor of the heavy-duty vehicle. In some instances,a plurality of battery packs may be individually mounted into cavitieswithin the floor of a vehicle.

In accordance with another aspect of the invention, the vehicle may havea composite body. The body may be substantially formed from at least onecomposite material, such as high strength fiber glass or carbon fiber.In some instances, the high stress areas of the vehicle body may beformed from a composite material. Alternatively, the vehicle body may beformed of a lightweight metal or metal alloy.

One or more battery strings may be provided as a propulsion power sourcein accordance with an embodiment of the invention. Each string mayinclude one or more battery pack. A battery pack may include one or moremodule, each of which may include one or more battery cell, such as alithium titanate battery cell. A battery management system may beintegrated at any level of a propulsion power source to provide sensorfeedback or any alarms or alerts. The housing for the propulsion powersource may include safety features, which may thermally or electricallyisolate components.

Other goals and advantages of the invention will be further appreciatedand understood when considered in conjunction with the followingdescription and accompanying drawings. While the following descriptionmay contain specific details describing particular embodiments of theinvention, this should not be construed as limitations to the scope ofthe invention but rather as an exemplification of preferableembodiments. For each aspect of the invention, many variations arepossible as suggested herein that are known to those of ordinary skillin the art. A variety of changes and modifications can be made withinthe scope of the invention without departing from the spirit thereof.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee.

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings:

FIG. 1 shows a schematic of a bus with various features in accordancewith one embodiment of the invention.

FIG. 2A shows an outline of a heavy-duty vehicle, such as a bus, withbatteries stored within the floor of the vehicle.

FIG. 2B shows an example of where batteries may be mounted into thefloor of a heavy-duty vehicle.

FIG. 2C shows an example of a battery arrangement.

FIG. 3 shows a high level outline of a battery arrangement that may beused as a propulsion power source in accordance with one embodiment ofthe invention.

FIG. 4 shows a schematic of a battery assembly that may be used topropel a heavy-duty vehicle.

FIG. 5 shows an example of a battery pack of a string.

FIG. 6 shows a high-level outline of a battery module.

FIG. 7 shows an example of a module in accordance with one embodiment ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides systems and methods for vehicle batteries.Vehicle battery systems for heavy-duty vehicles or high occupancyvehicles including buses, vans, and class 5-8 trucks, may compriselithium titanate batteries and may have various arrangements andconfigurations. Various aspects of the invention described herein may beapplied to any of the particular applications set forth below or for anyother types of vehicles or power sources. The invention may be appliedas a standalone system or method, or as part of an integrated vehiclesystem. It shall be understood that different aspects of the inventioncan be appreciated individually, collectively, or in combination witheach other.

Also, various aspects of the invention as described may be combined toprovide a heavy-duty hybrid electric vehicle where the batterypropulsion power source may deliver 12.5% or greater of the overallvehicle power. In various embodiments, the battery propulsion powersource may deliver 15% or greater, 20% or greater, 25% or greater, 30%or greater, 40% or greater, 50% or greater, 70% or greater, 80% orgreater, 90% or greater, 95% or greater, or substantially 100% of theoverall vehicle power. In one example, features such as a lightweightcomposite body, efficient drivetrain, and lightweight batteries may becombined such that the battery propulsion power source may deliver alarge percentage of the vehicle power requirement.

FIG. 1 shows a schematic of a bus with various features, in accordancewith one embodiment of the invention. The features of the bus may beapplied to other heavy-duty or high occupancy vehicles, wherein“heavy-duty vehicles” may include a transit bus, a school bus, adelivery van, a shuttle bus, a tractor trailer, a class 5 truck(weighing 16,001-19,500 lbs., two-axle, six-tire single unit), a class 6truck (weighing 19,501-26,000 lbs., three-axle single unit), a class 7truck (weighing 26,001-33,000 lbs., four or more axle single unit), aclass 8 truck (weighing 33,000 lbs. and over, four or less axle singletrailer), a vehicle with a GVWR weighing over 14,000 pounds, a vehiclewith a cargo to driver mass ratio of 15:1 or greater, a vehicle with sixor more tires, a vehicle with three or more axles, or any other type ofhigh occupancy or heavy-duty vehicle.

A heavy-duty vehicle may have a propulsion power source, which includesbatteries. In some embodiments of the invention, the heavy-duty vehiclemay have one or more additional power sources, such as a combustionengine or a fuel cell. The heavy-duty vehicle may be an electricbattery-powered vehicle or a hybrid electric vehicle, and may be able touse the same basic battery configuration, drive motor, and controller,regardless of whether the vehicle is an all-battery vehicle or a hybridvehicle.

In some embodiments, a heavy-duty vehicle may travel a predeterminedroute, and stop at predetermined points for recharging. See, e.g., U.S.Pat. No. 3,955,657, which is hereby incorporated by reference in itsentirety.

Propulsion Power Source

In one embodiment of the invention, the propulsion power source of aheavy-duty vehicle may include lithium titanate batteries. In someimplementations, the propulsion power source may include batteries thatare only lithium titanate batteries, without requiring any other typesof batteries. The lithium titanate batteries may include any format orcomposition known in the art. See, e.g., U.S. Patent Publication No.2007/0284159, U.S. Patent Publication No. 2005/0132562, U.S. PatentPublication No. 2005/0214466, U.S. Pat. Nos. 6,890,510, 6,974,566, and6,881,393, which are hereby incorporated by reference in their entirety.

The use of lithium titanate batteries may enable rapid charging of avehicle, and a long battery life. In some embodiments of the invention abattery propulsion power source may be able to charge to a very highstate of charge within minutes. For instance, in a preferableembodiment, the power source may be able to charge to over 95% state ofcharge within ten minutes. In other embodiments of the invention, abattery propulsion power source may be able to charge to over 65% stateof charge, over 70% state of charge, over 75% state of charge, over 80%state of charge, over 85% state of charge, over 90% state of charge, orover 95% state of charge within ten minutes, or nine minutes, sevenminutes, five minutes, three minutes, or one minute.

In some implementations, a battery propulsion power source may becharged using a periodic off board charging connection. An off boardcharging system may be a battery charging system externally located froma vehicle. In an alternate implementation, a battery propulsion powersource may be charged by using an on board power generation device. Anonboard power generation device may be any power generation device thatmay be brought onto a vehicle or incorporated into a vehicle, which mayincorporate various means to charge a battery.

In accordance with another embodiment of the invention, the propulsionpower source may include batteries with any battery chemistry known inthe art or later developed. Such electric or hybrid electric vehiclebatteries may include, but are not limited to, lead-acid (“flooded” andVRLA) batteries, NiCad batteries, nickel metal hydride batteries,lithium ion batteries, Li-ion polymer batteries, zinc-air batteries ormolten salt batteries. In some implementations, battery storage capacitymay be within the 18 to 100 kWh capacity range.

In some alternate embodiments, the propulsion power source may include acombination of lithium titanate batteries and other types of batteriesor ultra capacitors.

A charge/discharge control circuit may receive measurement signals fromsensors of the batteries, such as temperature sensors, voltmeters andammeters. Based on the input signals the control circuit can compute thepresent charge capacity, and can set a certain state of charge (SOC),and thereby control the charge/discharge of the batteries of the powersource. A battery may receive power from an external or internal powersource.

The battery power source of a heavy-duty vehicle may include anelectrode group with a spiral structure formed of a positive electrode,negative electrode and separator between the positive and negativeelectrode. The electrode group may be formed by winding the positiveelectrode and negative electrode with the separator, and then subjectingthe resultant structure to thermal pressing. Alternatively, the positiveelectrode, negative electrode and separator may be formed by using anadhesive polymer. A positive terminal can be electrically connected tothe positive electrode. Similarly, a band-shaped negative terminal canbe electrically connected to the negative electrode. The electrode groupmay be contained in a container with the ends of the positive andnegative terminals made to protrude from the container to form a batterycell.

The battery may include a negative electrode comprising a negativecollector, and a negative-electrode layer provided on one or both sidesof the collector and containing a negative electrode active material,conductive agent and binding agent.

In accordance with some embodiments of the invention, the negativeelectrode may include an active material with a metal oxide, metalsulfide, metal nitride or metal alloy. In some implementations of theinvention, the negative electrode may include active materials for anybattery chemistry known in the art.

A preferable embodiment of the invention may include a negativeelectrode material containing a lithium titanium complex oxide. Lithiumtitanate oxides, such as (1) spinel-type Li_(4+x)Ti₅O₁₂, (x: −1≤x≤3, andpreferably, 0<x<1) or (2) ramsdellite-type lithium titanate, such asLi_(2+x)Ti₃O7 (x: −1≤x≤3) can be used. Lithium titanium complex oxidesmay include, in addition to lithium titanium oxides, titanium-basedoxides that do not contain lithium.

Lithium titanium oxides may include, for example, a metal complex oxidecontaining at least one element selected from the group of TiO₂, Ti, P,V, Sn, Cu, Ni and Fe. The TiO₂ may be of an anatase type and may havelow crystalline properties acquired at a thermal treatment temperatureof 300 to 500 degree C. As a metal complex oxide containing at least oneelement selected from the group of Ti, P, V, Sn, Cu, Ni and Fe,TiO₂—P₂O₅, TiO₂—V2O₅, TiO₂—P₂O₅—SnO₂, and TiO₂—P₂O₅-MeO (Me is at leastone metal selected from the group consisting of Cu, Ni and Fe), etc.,can be exemplified. In some cases, the metal complex oxide can have lowcrystalline properties, and a microstructure in which a crystallinephase and amorphous phase are mixed, or only an amorphous phase exists.By virtue of this microstructure, the cycle performance can besignificantly enhanced. In particular, a metal complex oxide containinga lithium titanium oxide and at least one element selected from thegroup of Ti, P, V, Sn, Cu, Ni and Fe is preferable.

In some implementations, the average grain size of the primary particlesof the negative-electrode material may be 1 μm or less. More preferably,the average grain size of the negative-electrode material may be 0.3 μmor less.

Vehicle Body

A heavy-duty vehicle may include any vehicle body composition andstructure known in the art. In some cases, a high occupancy orheavy-duty vehicle may have a body structure that may classify it as,for example, a transit bus, a school bus, a delivery van, a shuttle bus,a tractor trailer, or class 5-8 truck.

For example, a heavy-duty vehicle may have a body composed of a metalsuch as aluminum or steel, or alloys such as a magnesium alloy. Inpreferable embodiments of the invention, the vehicle may have alightweight, strong body.

The heavy-duty vehicle may also include a vehicle body including atleast one composite material. In some embodiments of the invention, theheavy-duty vehicle body may be substantially formed from at least onecomposite material. A composite material is preferably a lightweight,non-metallic material. For example, high stress areas of the vehicle maybe formed of a composite material such as carbon fiber, balsa and/orstructural foam core. In some examples, the bulk of the body may beformed of a high strength fiberglass, balsa and/or foam core.

Several alternate embodiments of the invention may include a vehiclebody where the body comprises a first skin, a second skin, and a corebetween the skins. For example, the core may comprise a honeycombstructure, or may be constructed from balsa wood or foam, or may includea composite material that is or is not the same as the first or secondskin materials. Other materials that may form various parts of thevehicle body may include aluminum, stainless steel, fiberglass, aramid,ultra high molecular weight polyethylene, carbon fiber, or other knownstructural fibers, fiber reinforced plastics or combination thereof.Other combinations of composite materials may be used for variouscomponents of the heavy-duty vehicle.

Composites may include materials that may cover a wide range ofstrength, from low-grade non-structural materials using short fibers ornon-oriented fibers with inexpensive resins, to high strength andstiffness properties utilizing woven cloth in a high performance resinsystem. Body panels may be structural elements, which have highstrength, and a preferred embodiment may utilize this type ofconstruction. The common materials for structural composites incommercial applications may include fiberglass, aramid, and carbon fibercloths and tapes in a vinyl ester or epoxy resin matrix. These materialsmay have different mechanical properties in terms of tensile strengthand stiffness, compressive strength and stiffness, impact resistance,etc. The composite materials can also be corrosion andmoisture-resistant when properly constructed.

By utilizing selected combinations of these materials with theseindividual properties, the vehicle body can achieve the desiredperformance characteristics of extremely high strength in the plane ofthe panel or at a right angle, high stiffness, and good impact strengthand durability. In some embodiments, the materials may includenon-composite materials, composite materials, or a combination thereof.Proper design and construction of these structural composite panels mayprovide all the necessary strength and stiffness to serve as the soleself-supporting structure of the vehicle chassis, even for intensiveurban service.

In some embodiments, the vehicle structure may include a lightweightskeletal frame with a plurality of body panels attached to the skeletalframe. In another embodiment, the body may be molded out of severalpieces or one piece.

In accordance with one embodiment of the invention, the floor structureof the vehicle may be substantially formed from at least one compositematerial. For example, the floor structure of the vehicle may besubstantially formed from carbon fiber or fiberglass. Alternatively, thefloor structure may be formed of a non-composite material such as ametal, which may include aluminum or steel. The floor structure may beformed of any material that may not burn when exposed to an electricarc, or relatively high heat.

Battery Location

FIG. 2A shows an outline of a heavy-duty vehicle, such as a bus, withbatteries stored within the floor of the vehicle. In accordance withsome embodiments of the invention, lithium titanate batteries may bemounted within a floor cavity of the vehicle. The batteries may bearranged into groupings that may be individually mounted into floorcavities from below or from the sides of the bus floor structure. Insome embodiments of the invention, there may be a plurality of cavitiesbelow the heavy-duty vehicle, which may be separated from one anotherand may contain one or more grouping of batteries. Alternatively, theremay be one cavity below the vehicle, which may contain the groupings ofbatteries.

FIG. 2B shows an example of where the batteries may be mounted onto thefloor of the heavy-duty vehicle, such as a bus. For example, each of thebattery packs may fit into a designated area in the floor of the bus.The battery system may be designed at a 6.75 inch height or less, whichmay allow it to fit under the floor of a low-floor transit bus. This mayallow for a completely low floor chassis with no compromise in theinterior seating layout. The bus may have a “true low floor”configuration, such that the bus may have a level floor way throughoutthe area between the axles of the bus, with energy storage mountedunderneath. For example if a bus has two axles, the floor between thetwo axles may be level and flat between the two axles. This may alsoapply to heavy duty vehicles with two or more axles; the floor betweenany of the axles may be level and flat. This may indicate that the floorof the bus may not have protrusions to accommodate the underlyingbatteries; the batteries may lie flat beneath the floor of the bus. Thismay contrast with traditional buses, which have boxes underneathpassenger seats for the energy storage system, which comprises seatinglayouts. The battery system may have a height of 8 inches or less, 7.25inches or less, 7 inches or less, 6.875 inches or less, 6.75 inches orless, 6.625 inches or less, 6.5 inches or less, 6.375 inches or less,6.25 inches or less, 6 inches or less, five inches or less, four inchesor less, or three inches or less.

In some embodiments, each battery pack may have its own compartmentwithin the floor of the bus. In some instances, each battery pack may bephysically isolated from the other battery packs. Some of the batterypacks may be electrically connected to one another in a string, but mayotherwise but electrically isolated from one another.

In alternate embodiments of the invention, the batteries may beintegrated into other parts of the heavy-duty vehicle. For example, thebatteries may be mounted on the front, rear, top, or side of thevehicle. In some implementations, the batteries may be distributed overdifferent locations on the vehicle. For example, some of the batteriesmay be stored within the floor of the vehicle while some of thebatteries may be stored on the top of the vehicle. Any combination ofbattery storage locations may be used.

The propulsion power source for a heavy-duty vehicle may include one ormore battery assembly. A battery assembly may provide high voltage powerto the traction motor, high power accessories, and low voltageaccessories in the vehicle through the use of a converter. In oneimplementation of the invention, a large capacity (e.g., 50 Ah) cell ina series string of batteries in parallel may be safer to operate in theevent of a failure than a parallel set of cells in series. Becauselithium cells typically fail-short, if the cell was in parallel withmany other cells, the other cells could discharge as much energy as isavailable into the damaged cell. In some cases, cells may be put inparallel first to reduce cost of battery management systems since eachcell voltage may be measured. However, in some other embodiments, withlarger capacity cells, paralleling batteries before placing them inseries may not be necessary. The use of larger capacity cells mayincrease the safety of the entire assembly without adding cost to thebattery management system. Thus, batteries may be arranged in series orparallel, or any combination thereof. Such battery connectionflexibility may also allow flexibility in battery placement. Suchflexibility of battery placement may be beneficial wherever thebatteries are distributed on the vehicle.

In addition, the use of a composite material, or non-burningnon-composite material, for the vehicle may allow flexible battery packplacement. In the event of a low-floor design of a heavy-duty vehicle,the height of the batteries may be a constraint. For example, in someembodiments, such as a low floor transit or school bus, the batteriesmay need to be maintained to less than 6.75″ in height. Integrating thebattery packs into the floor of a vehicle may keep the center of gravityof the vehicle much lower and balance weight distribution, thusincreasing drivability and safety.

Battery Arrangement

FIG. 2C shows an example of a battery arrangement. A module may fitwithin a battery pack, which may fit within a battery assembly, whichmay include strings of battery packs connected in series.

FIG. 3 shows a high level outline of a battery arrangement, which may beused as a propulsion power source in accordance with one embodiment ofthe invention. The battery assembly in a vehicle may be designed to haveany number of main battery strings. For example, in embodiment, thebattery assembly may include three main battery strings. Each string mayconsist of a number of battery packs. For example, there may be twopacks per string. Each string may or may not have the same number ofpacks. For example, each string may have two packs. In another example,one string may have two packs, another string may have one pack, andanother string may have five packs. The strings may be arranged so thatthey are connected in parallel. Alternatively, the strings may allow thepacks to be connected in series.

A battery management system (BMS) may be integrated into the packsand/or modules to give early warning to potential problems with weakerbattery cells within a string. The BMS can give accurate feedback oncell voltages and temperatures within the modules in order to ensure ahealthy battery pack. If there are any problems with a particularstring, those modules can be automatically removed from service and thevehicle can operate on reduced capacity until the end of the day ifnecessary. The BMS can disconnect a battery string if a fault isdetected. Even if an entire battery string is connected, the vehicle iscapable of operating.

FIG. 4 shows a schematic of a battery assembly that may be used topropel a heavy-duty vehicle, such as a bus, in accordance with oneembodiment of the invention. In some cases, the packs may beelectrically arranged in a staggered configuration to match cablingresistances and ensure similar operation of each string. One example ofa staggered configuration is a group of four packs (pack 1, pack 2, pack3, pack 4 lined up from near to far), that are arranged into twostrings. The first string may connect pack 1 and pack 4 together, whilethe second string may connect pack 2 and pack 3 together. Each pack mayhave the same amount of wire connecting the two batteries even if eachpack is a different distance from the junction area. Each pack may beindividually mounted from below the vehicle into one, two, or morecavities built into the floor.

A pack may include boxes or containers that enclose the contents of thepack. The containers may have any shape or configuration that may enablethem to hold the contents of the battery pack. The containers may bewatertight and may be formed of a material that will not oxidize or burnwhen exposed to an electric arc. For example, the material for thecontainers may be a 3CR12 stainless steel to protect against corrosionfrom road salts, inhibit oxidation when in contact with an electric arc,and help with material fatigue. Other materials, such as compositematerials, may be used that may have similar features.

Battery Pack Design

FIG. 5 shows an example of a battery pack of a string. A battery packmay include one or more modules. For example, battery packs may eachcontain eight modules. Each battery pack of a battery assembly may ormay not include the same number of modules. For example, one batterypack may include six modules, while another battery pack may includeeight modules, while another battery pack may also include eightmodules.

The pack design may accommodate safety and size. In a pack design, anumber of factors may be considered including detection, containment,isolation, and suppression. Each of these areas may address a group ofpotential problems that could occur and may help to meet all applicableFederal Motor Vehicle Safety Standards.

A BMS may be a primary detection method of a problem with a particularcell, module, pack, or string. The BMS may detect when a failure occursand may be able to direct the battery assembly to disconnect portions ofthe battery assembly, such as individual battery strings, where thefailure may have occurred, in order to prevent other portions of thebattery assembly from being compromised and to allow continuousoperation of the vehicle. The BMS may communicate with and within eachpack to achieve the desired level of detection and management.

The pack may be watertight and may provide containment. The pack may becontained within a container or box that may protect the pack fromexternal elements that may damage the contents of the pack. The packcontainer may be designed to protect the pack for a long period of time.In addition to protecting the contents of the pack from externalthreats, the container of a pack may contain any failures that may occurwithin a pack, in order to prevent damage to other packs or portions ofthe vehicle.

Dividers between the modules may protect modules from other modules thatmay have a failure, thus providing isolation. If a module were to fail,the dividers may protect other modules from the failed module. Thedividers may or may not be integrated into the pack container structureand may be made of a material that may not oxidize when exposed toelectrical arcs or high temperatures. FIG. 2C shows an example of a packcontainer with module dividers.

Suppression may not necessary due to the very limited airspace withinthe enclosure. In some cases, suppression configurations may be added,which may require providing an exhaust path for the suppressionmaterial. The exhaust path may consist of an opening drilled in asection of the pack with a spring-return shield and a gasket material toseal the exhaust opening when it is not in use.

In some embodiments, a battery pack may include modules with integratedheat sinks, cooling features such as a cooling plate, module retainers,buss bars to attach modules together, and one or more small compartmentsthat may house the BMS boards, relays, and fuses. The compartment may ormay not be substantially thermally and/or physically isolated from themodules. Interconnection wiring may run to a watertight connector in thesmall end-box that can disconnect power to the relay, thus making theterminals of the connector safe when the main cable is disconnected. Thepack may include integrated cooling features in addition to coolingfeatures of the modules. In some implementations, integrated coolingplates can provide cooling from a main vehicle electrical coolingsystem. In some embodiments, the cooling plates may preferably bemaintained below 43° C. for operation of the batteries. Other coolingfeatures known in the art, such as various heat sink arrangements or useof convection cooling may be used in a battery pack. Active coolingtechniques, such as fluid cooling, which may utilize fans, the passageof air, liquid, or other fluids, may also be utilized.

A thermal shield consisting of a spray-on ceramic coating on the lowestpoint of the packs may be applied to packs exposed to the underside ofthe vehicle or anywhere else where radiated heat may be a concern.

Such a battery pack design may have the following benefits: low costintegration, design for safety, ease of assembly, may be maintenancefree, and may have simple mounting.

Battery Module Design

FIG. 6 shows a high-level outline of a battery module. A battery modulemay include one or more battery cells. In a preferable embodiment, thebattery cells may be lithium titanate battery cells. In otherembodiments, the battery cells may have other battery chemistries knownin the art. For example, each module may comprise ten battery cells.Each module may or may not include the same number of battery cells. Forexample, one module may include eight battery cells, while anothermodule may include twelve battery cells, and another module may includethirteen battery cells, while yet another module may include thirteenbattery cells.

The cells may have any arrangement or connection within the module. Forexample, the cells may all be connected in series. Alternatively, thecells may be connected in parallel. Or in some cases, the cells may beconnected in a combination of series or parallel within the module.

The battery cells may have various specifications, such as variousvoltages. For example, each cell for a lithium titanate battery may beat 2.3 V_(nominal), 50 Ah giving a nominal energy of 115 Wh. Each cell,such as lithium ion batteries or other types of batteries, may or maynot vary in its specifications. In some embodiments, the cells may beprismatic cells. Each prismatic cell may be housed in a specializedMylar/foil pouch and may be somewhat fragile. The module housing can bedesigned to and protect the cells from outside damage, making themeasier to handle, and providing cooling support.

The modules may include cooling features. For example, modules may haveintegrated aluminum cooling fins placed between each cell. In otherexamples, cooling plates may all link up to an anodized aluminumbackplane that can then be cooled to support even cooling through themodule. Other cooling features known in the art may be used, such asvarious heat sink arrangements, forced convection cooling, and so forth.

FIG. 7 shows an example of a module in accordance with one embodiment ofthe invention. The case of a module may be made of an ABS material thatcan be easily machined and produced very rapidly. In otherimplementations, the case of a module may be of other materials, such asa composite material, fiberglass, or carbon fiber. In some examples, thecase may be made from a material that may provide some level ofisolation, such as a material that may not burn when exposed to anelectric arc. A front weld plate can be included to accurately locateand hold the terminals to the case to reduce fatigue stress cracks inthe cell tabs. In some cases, the cell tabs may be made of a metal, suchas aluminum. BMS connectors can be integrated into the front of themodule for quick connection of an off-board BMS. Terminals may be offsetand tapped for vertical installation of attachment bolts and ease ofassembly.

Modules must be isolated from each other to protect against potentialshort-circuiting. This can be accomplished through careful materialselection and post processing of the heat sinks. If a short is everdetected through the BMS, the system may disconnect each pack in thestring, which can isolate the fault. This level of safety may beincluded in the event of a major crash or failure of the isolationsystem.

It should be understood from the foregoing that, while particularimplementations have been illustrated and described, variousmodifications can be made thereto and are contemplated herein. It isalso not intended that the invention be limited by the specific examplesprovided within the specification. While the invention has beendescribed with reference to the aforementioned specification, thedescriptions and illustrations of the preferable embodiments herein arenot meant to be construed in a limiting sense. Furthermore, it shall beunderstood that all aspects of the invention are not limited to thespecific depictions, configurations or relative proportions set forthherein which depend upon a variety of conditions and variables. Variousmodifications in form and detail of the embodiments of the inventionwill be apparent to a person skilled in the art. It is thereforecontemplated that the invention shall also cover any such modifications,variations and equivalents.

What is claimed is:
 1. A low-floor electric bus comprising: a body; afloor; and a plurality of battery packs mounted under the floor of thelow-floor electric bus such that (a) one or more of the plurality ofbattery packs form exposed surfaces of an underside of the low-floorelectric bus and (b) between a front axle and a rear axle of the bus,the floor inside the bus under passenger seats is substantially levelwith the floor not under the passenger seats, wherein each battery packof the plurality of battery packs includes a cooling plate adapted tocool the battery pack.
 2. The low-floor electric bus of claim 1, whereineach battery pack of the plurality of packs has a height of 8 inches orless.
 3. The low-floor electric bus of claim 2, wherein each batterypack of the plurality of battery packs has a height of 6.75 inches orless.
 4. The low-floor electric bus of claim 1, wherein each batterypack of the plurality of battery packs includes a box that enclosescontents of the battery pack.
 5. The low-floor electric bus of claim 1,wherein each battery pack of the plurality of battery packs includesmultiple battery modules, and each battery module includes multiplebattery cells.
 6. The low-floor electric bus of claim 1, wherein eachbattery pack of the plurality of battery packs is positioned in a cavityunder the floor.
 7. The low-floor electric bus of claim 1, wherein theplurality of battery packs includes a plurality of lithium titanatebattery packs.
 8. The low-floor electric bus of claim 1, wherein thecooling plate is adapted to cool the battery pack using active cooling.9. The low-floor electric bus of claim 1, wherein the cooling plate isadapted to circulate a fluid therethrough.
 10. The low-floor electricbus of claim 1, further including a thermal shield on a side of theplurality of battery packs opposite the floor.
 11. A low-floor electricbus, comprising: a body; a floor; and a plurality of battery packspositioned under the floor of the low-floor electric bus such that thefloor has a low-floor configuration, wherein the floor inside the busbetween a front axle and a rear axle is substantially flat and one ormore of the plurality of battery packs form exposed surfaces of anunderside of the low-floor electric bus, and wherein each battery packof the plurality of battery packs is fluidly coupled to a cooling systemof the bus.
 12. The low-floor electric bus of claim 11, wherein theplurality of battery pack include one or more lithium titanate batterypacks.
 13. The low-floor electric bus of claim 12, wherein the pluralityof battery packs include at least one battery pack having a chemistrydifferent from the one or more lithium titanate battery packs.
 14. Thelow-floor electric bus of claim 12, wherein each battery pack of the oneor more lithium titanate battery packs has a height of 8 inches or less.15. The low-floor electric bus of claim 11, wherein each battery pack ofthe plurality of battery packs includes multiple battery modules, andeach battery module includes multiple battery cells.
 16. The low-floorelectric bus of claim 11, wherein the one or more cavities permitmounting of the plurality of battery packs into the one or more cavitiesfrom below an underside of the low-floor electric bus.
 17. A low-floorelectric bus, comprising: a body; a drive motor; a bus cooling system; afloor; and a battery power source configured to provide power to thedrive motor, the battery power source including a plurality of batterypacks under the floor of the low-floor electric bus such that the floorinside the bus in an area that extends the width of the bus between afront axle and a rear axle is substantially flat and one or more of theplurality of battery packs form exposed surfaces of an underside of thelow-floor electric bus, wherein each battery pack of the plurality ofbattery packs is fluidly coupled to the bus cooling system.
 18. Thelow-floor electric bus of claim 17, wherein each battery pack of theplurality of battery packs have a height of 8 inches or less.
 19. Thelow-floor electric bus of claim 17, wherein each battery pack of theplurality of battery packs is mounted in a cavity formed under thefloor.
 20. The low-floor electric bus of claim 17, wherein the pluralityof battery packs includes one or more lithium titanate battery packs.